IP address and Subnetting

If the CIDR value is /25 then subnet mask will be – 255.255.255.128. In binary – 11111111.11111111.11111111.10000000 (8+8+8+1 = 25)

Same way if subnet mask is – 255.255.192.0 the CIDR value will be /18 (8+8+2)

Wild card calculation –

Whatever the subnet mask minus it with 255. E.g. – mask 255.255.0.0 wildcard will be 0.0.255.255

Supernet calculation –

Sometimes we set lesser subnet mask or cidr value than the default value & apply it on ACL, Prefix-list or route advertisement. This will help us to just select 1 master subnet & all child subnet will be select. Example –

172.16.0.0/12 – This will select 172.16.0.0 to 172.31.0.0 B. 192.168.0.0/ 13 will select 192.168.0.0 to 192.175.255.255